Ensure that def-side physreg copies are scheduled above any other uses

so the scheduler can't create new interferences on the copies
themselves. Prior to this fix the scheduler could get stuck in a loop
creating copies.
Fixes PR9509.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128164 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index aa93bba29d210d4adccd52ad5d339022c2db8a81..f02d78f6134d526886a0a203cf937c8ca70436d4 100644 (file)
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -935,6 +935,15 @@ void ScheduleDAGRRList::InsertCopiesAndMoveSuccs(SUnit *SU, unsigned Reg,
       AddPred(SuccSU, D);
       DelDeps.push_back(std::make_pair(SuccSU, *I));
     }
+    else {
+      // Avoid scheduling the def-side copy before other successors. Otherwise
+      // we could introduce another physreg interference on the copy and
+      // continue inserting copies indefinitely.
+      SDep D(CopyFromSU, SDep::Order, /*Latency=*/0,
+             /*Reg=*/0, /*isNormalMemory=*/false,
+             /*isMustAlias=*/false, /*isArtificial=*/true);
+      AddPred(SuccSU, D);
+    }
   }
   for (unsigned i = 0, e = DelDeps.size(); i != e; ++i)
     RemovePred(DelDeps[i].first, DelDeps[i].second);